In the field of graphic arts, an image formation system capable of giving the photographic characteristic of ultra-high contrast (especially having a gamma value of 10 or more) is required, and must be sufficient to attain a good reproduction of a half-tone image of continuous tone as well as a good reproduction of a line image.
A specific developer called a lith developer has heretofore been used for said purpose. The lith developer contains only hydroquinones as a developing agent, and uses a sulfite as preservative in the form of an adduct of a sulfite with formaldehyde in order not to deteriorate the infectious developability thereof. The concentration of the free sulfite ion in said developer is kept extremely low (generally, 0.1 mole/l or less). Thus, the lith developer extremely easily suffered aerial oxidization and cannot last more than three days, which is a serious defect.
Methods for obtaining the photographic characteristic of high contrast by the use of a stable developer and a hydrazine derivative are disclosed in U.S. Pat. Nos. 4,224,401, 4,168,977, 4,166,742, 4,311,781, 4,272,606, 4,211,857 and 4,243,739. According to said methods, the photographic characteristic of ultra-high contrast and high sensitivity may be obtained, and moreover, addition of a sulfite of high concentration to a developer is possible. Accordingly, the stability of the developer against aerial oxidation is markedly improved, as compared to the lith-developer.
These conventional methods using a hydrazine derivative, however, have some problems in that the sensitivity and the gradation of light-sensitive materials are lowered when said materials are preserved for a lapse of time. In addition, if some conventional sensitization means are applied to the light-sensitive materials in order to improve the sensitivity thereof (for example, the grain size of silver halide grains contained therein are made larger, or the light-sensitive materials are sensitized with a novel metal sensitizer), a problem occurs known as "black spots" in this technical field. The "black spots" are those appearing in non-image parts (for example, among half-tone dots), which markedly occur when the pH value of the developer to be used becomes higher after being preserved for a lapse of time and thus fatigued. The occurrence of such "black spots" extremely lowers the quality of photographs.